1) Field of the Invention
The invention relates to a process for the preparation of bitumen/polymer compositions with a reinforced multigrade character. It also relates to the application of the compositions obtained to the production of bitumen/polymer binders for surfacings and especially for road surfacings or for leakproof facings.
2) Background Art
Bitumen/polymer compositions with a reinforced multigrade character are intended, according to the invention, to mean bitumen/polymer compositions which have a wide plasticity range. The said range is defined as the difference between the ring-and-ball softening temperature (abbreviated to RBT), which reveals the properties of the binder or bitumen/polymer composition when heated, and the Fraass brittle point, which reveals the properties of the bitumen/polymer composition when cold. The wider the plasticity range, the better will the bituminous binder consisting of, or based on, the bitumen/polymer composition resist stresses when heated and when cold.
The abovementioned values of the ring-and-ball softening temperature (RBT) and Fraass brittle point are determined by standardized procedures as shown below:
ring-and-ball softening temperature: determined according to NF standard T 66 008 and expressed in .degree.C.; PA1 Fraass brittle point: determined according to NF standard T 66 026 and expressed in .degree.C.
Crosslinking, using sulphur, of elastomers bearing unsaturations, especially copolymers of styrene and of a conjugated diene such as butadiene or isoprene, within bitumens produces bitumen/polymer compositions which have an improved stability and excellent physicomechanical characteristics, and which can be employed for the production of various dressings, especially road surface dressings, bituminous mixes or else leakproof facings exhibiting improved characteristics when compared with the dressings obtained from bitumens alone.
The preparation of bitumen/polymer compositions of the abovementioned type, in which the sulphur-cross-linkable elastomer is a copolymer of styrene and of a conjugated diene, is described, in particular, in references FR-A-2376188, FR-A-2528439 and EP-A-0360656.
It is also known that the properties of bituminous compositions consisting of mixtures of bitumens and of block copolymers of styrene and of a conjugated diene, especially block copolymers of styrene and of butadiene, can be improved by incorporating into said compositions a small quantity of a nonoxidizing. inorganic acid such as phosphoric acid (DE-A-2255173). The results obtained can be improved if the acid is added to the bitumen before the block copolymer is incorporated into it (U.S Pat. No. 5070123).